It is known in the art to prepare articles, particularly filaments and ribbons, having a high tensile strength and modulus, starting from solutions of high-molecular weight polymers, particularly high-molecular weight linear polyethylene. See, for instance, U.S. Pat. Nos. 4,344,908, 4,422,993, 4,430,383, 4,411,854 and 4,436,689. In these known processes, a solution of mostly below 30% by weight of a high-molecular weight polymer, particularly polyethylene, is passed through a round or slit-shaped spinning aperture at an elevated temperature to produce a filament or ribbon. The solution spun as a filament or ribbon solution is subsequently transformed into a gel filament or gel ribbon by cooling, after which it is stretched at an elevated temperature, either with or without removal of all or part of the solvent.
These known processes start from relatively dilute polymer solutions because it has been found that the stretchability and the final modulus and tensile strength of the articles are higher when the initial concentration of the polymer solution is lower.
A disadvantage is, however, that it is necessary in these processes to prepare a dilute homogeneous polymer solution to form the product, which is known to be costly in the manufacture of these products. In fact, a substantial portion of the plant manufacturing process costs for the production of articles starting from a polymer solution containing a large quantity of solvent is for the handling of the solvent. In particular, the processing equipment suitable for and required to accommodate the solvent handling is a major capital cost factor.
A further disadvantage of these dilute solution processes is that the rate of production is determined by the rate of spinning or extrusion, and this in turn is affected by the concentration of the solution.